Process for manufacturing small parts



United States Patent PROCESS FOR MANUFACTURING SMALL PARTS FROM THINMETALS Alfred E. Heath, Bordentown, N. 1., assignor to Radio Corporationof America, a corporation of Delaware No Drawing. Application October27, 1954, Serial No. 465,127

6 Claims. Cl. 95-'-5.7)

This invention relates generally to the manufacture of small parts fromvery thin metals and, more particularly, to an etching process forobtaining small metal parts from a sheet of thin metal which will notwithstand any mechanical working.

In the preparation of metal laminations, such as are used in magneticrecording heads for example, 'the laminations must be constructed of avery thin metal which is processed to have certain magnetic propertieswhich are believed to be a function of the internal molecular structureof the metal. Such metals will not Withstand any mechanical workingbecause such working disturbs the internal molecular structure resultingin a change of the magnetic properties of the metal and would require areprocessing of the metal. It is desired therefore to provide amanufacturing process bywhi'ch such laminations may be obtained from asheet of such prepared metal and during which process the metal will notbe Subjected to undue strain or distortion.

The photo-etch process which is frequently employed in the manufactureofmetal parts, is readily adaptable to the manufacture of theselaminations. However in the process of etching the metal, a suitablebacking must be provided to support the metal during the etching processand from which the small metal parts may be readily separated withoutbeing distorted.

Several attempts have previously been made to provide suitable etchresistive backings for the metal during the etching process. Gluing themetal to 'a phenolic board has been tried and rejected because in theseparation of the laminations from the board they were bent to such adegree as to make them useless. Several methods of applying etchresistive backings comprise painting a heavy coat of acetate cement orpaint on the back of the metal, or gluing paper or acetate cloth on theback of the metal. The method of removel of these backing's is todissolve the backing in a suitable solvent. The use of such backin-gshas several disadvantages. They do not provide the stiffness requiredfor etching in a paddle type eteher and the time involved for dissolvingthe backing and the number of washes required to clean the metal of theresistive backing material make the process unwieldy.

It is also desirable to provide a process for the manufacture of thesesmall laminations which is readily adaptable to automation 'or assemblyline methods.

An object bf this invention is to provide an improved process for thepreparation of small metal parts by the photo-etch method which permitsdistortion free separation of the metal parts from their backing.

Another object of this invention is to provide an improved process forbacking a metal sheet which provides the stiffness necessary for etchingthe metal and permits easy removal of the finished parts from thebacking.

A further object of this invention is to provide an improved process forthe manufacture of thin metal laminations which is rapid andinexpensive.

A still further object of the present invention is to pro- .vide animproved process for the manufacture of thin 2,735,763 Patented Feb. 21,1956 metal laminations which process is adaptable to automatic assemblyline methods.

In general the improved process comprises conditioning a surface of themetal, coating this surface with a photosensitive resist emulsion,exposing and developing the photo-resist, coating the untreated side ofthe metal with a substantial thickness of wax, etching the metal in asuitable etcher, and separating the metal parts from the wax backing byexposing the wax and adhering metal parts to a cold atmosphere ormedium.

The novel features of the invention, as well as additional objects andadvantages thereof, will be understood more fully from the followingdetailed description.

In the preparation of a metal for the photo-etch process the metal isfirst thoroughly cleaned by means of a tnchlorethylene degreaser forexample. The cleaned metal may be chemically etched, by means of nitricacid for example, to roughen the surface in order that a coating mayreadily adhere thereto. The metal sheet is next placed in contact with asuitable backing, such as a Bakelite panel for example, and aphoto-sensitive resist is caused to flow over one surface of the metalto completely cover the surface. The photo-sensitive resist is anemulsion which is applied as a coating to a surface and which will reactto light of a predetermined intensity. After the coating has set, if aportion of the coating is exposed to light, the exposed portionundergoes a chemical change which causes it to resist dissolution bycertain reagents which will dissolve the unexposed portions.

The sheet is then placed in a heating oven in order to harden thiscoating. The metal sheet is next placed on a clean backing, a Bakelitepanel for example, and is covered with a negative. In the instant casethe negative would be comprised of an opaque screen provided withtransparent lamination patterns. These materials are then placed on asuitable exposure apparatus and exposed to light for a fixed perioddetermined by the particular photoresist material. The exposed metal isthen developed by spraying the exposed surface with a suitable solvent.The portion of the photo-sensitive coating which has been exposed to thelight, namely the lamination patterns, will resist the action of thissolvent and continue to adhere to the metal while the portion of thephoto-resist which has not been exposed will be dissolved and washedaway from the metal to again bare the metal between the laminationpatterns.

The metal is now ready to be etched to produce the desired parts fromthe sheet. To provide the backing in accordance with the invention forthe metals during the etching process, a sheet is laid face down on aglass plate or other smooth surface. A form is provided along the edgeof the sheet and softened or molten wax is poured over the sheet withinthe form. A thickness of 3/ 32 to .4; inch has been found satisfactory.Two waxes which have been successfully employed in this process areCerise AAA, a product of Socony Vacuum, and Sunwax 1290, a product ofthe Sun Oil Company. Both of these waxes are mineral base waxes.

By way of example, brass bars have been used to provide the form aroundthe perimeter of the metal sheet to retain the wax when it is poured.This form serves as a mold or dam. It is desirable to treat the mold ordam with a mold release compound such as silicone grease in order thatthe mold may be readily removed after the wax has set. After the Wax hasset, the form is removed and the wax backed sheet is then placed in apaddle type etcher, for example. This etcher causes an etching solutionto be splashed over the metal and to dissolve the metal where it is notprotected by the photo-resist coating. At the completion of the etchingprocess, there exists the sheet of wax with the desired laminationsadhering to one surface.

The critical point of the entire process is the separation of theselaminations from the wax without bending or distorting them. This isaccomplished by causing the wax to be supercooled to a temperatureconsiderably below freezing and preferably to a point where the waxbecomes brittle. Due to the difference in the coefficients of expansionof the two materials, wax and metal, one will contract more rapidly thanthe other causing the laminations to loosen themselves from the wax.

The cooling may be accomplished by merely placing the wax backedlaminations in a cooling compartment. It has been found in practicingthe present invention that the time required to cool the materialssufiiciently to produce the desired result is too long. An effectivemeans of accomplishing rapid cooling is to dip the wax into liquidacetone which has been cooled by the introduction of Dry Ice. Acetone israpidly cooled to a temperature of 70 C. by this method. A dipping for aperiod of not more than 5 seconds is sufficient. Other liquids which maybe cooled to other temperatures would be equally effective.

The use of Dry Ice, which is solidified carbon dioxide, as a coolingagent for the liquid has an additional beneficial effect. When therelatively warm wax is placed in the cold liquid, it causes a bubblingaction of the carbon dioxide which is in the liquid adjacent the Wax andthis bubbling aids in freeing the laminations from the wax after theyhave initially broken loose due to contraction. Artificial agitation ofthe liquid will also serve to accomplish this result.

Another advantage in using a liquid as the cooling agent is that thelaminations may be easily recovered from the liquid by providing a sievetype basket to collect the laminations as they drop away from the waxsurface.

The final step in the process is to place the laminations in a solventwhich removes the photo-resist coating therefrom.

It will be apparent that the above described process is a relativelysimple process which is inexpensive and rapid in relation to otherprocesses indicated herein. The process is also readily adaptable toproduction line methods since all of the steps are relatively simple.

What is claimed is:

1. In a process for manufacturing small parts from a thin sheet ofmetal, the steps comprising coating a surface of said sheet with alight-sensitive resist, exposing said coated surface to a light image inthe nature of a pattern, removing the unexposed resist, backing saidsheet with a substantial thickness of wax, etching away the metal sheetuncovered by the removed resist, and supercooling the wax backed partsthereby causing the parts to be released by the wax.

2. A process for manufacturing small parts from a sheet of thin metalcomprising coating a first surface of said metal sheet with a lightsensitive resist emulsion, exposing a portion of said emulsion through anegative having opaque portions, washing the unexposed portions of saidemulsion from said surface, applying a backing of wax to a secondsurface of said metal sheet, etching completely away the portions ofsaid sheet uncovered by the removed, unexposed emulsion thereby leavingmetal parts adhering to said wax, and dipping the wax backed metal partsin a supercooled liquid whereby the parts are separated from saidbacking.

3. A process for manufacturing small laminations from a sheet of thinmetal comprising applying a coating of light-sensitive resist emulsionto one surface of said sheet,

placing a negative having transparent lamination patterns over saidsurface, exposing said coated surface to light through said negative toprovide exposed and unexposed portions of said emulsion, washing awaythe unexposed portions of said emulsion, applying a relatively thicklayer of wax to the uncoated surface of said metal sheet, completelyetching away the portions of the metal sheet uncovered by the removed,unexposed emulsion thereby leaving the laminations adhering to said wax,and dipping said wax into a supercooled liquid thereby causing saidlaminations to separate from said wax.

4. A process for manufacturing small laminations from a sheet of thinmetal comprising applying a coating of light sensitive resist emulsionto one surface of said sheet, placing an opaque negative havingtransparent lamination patterns over said coated surface, exposing saidcoated surface to light through said negative, developing said exposedsurface which comprises washing away the portions of said coating notexposed to light, applying a relatively thick backing of wax to theuncoated surface of said metal sheet, completely etching away theportions of the metal where the resist emulsion has been washed awaythereby leaving the laminations adhering to the wax, and dipping saidwax into a supercooled liquid thereby causing said laminations toseparate from said wax due to different rates of contraction.

5. A process for manufacturing small metal laminations from a sheet ofthin metal comprising cleaning a first surface of said metal, coatingsaid first surface with a photo-sensitive resist emulsion, placing anopaque negative having transparent lamination patterns over said coatedsurface, exposing said coated surface to light through said negative,exposing said coated surface to a developing medium which dissolves andwashes away said photo-sensitive resist which has not been exposed tolight thereby uncovering portions of said first surface, applying arelatively thick coating of wax to a second surface of said sheet toform a rigid backing for said sheet, exposing said first surface to anetching medium thereby completely etching away the uncovered portion ofsaid sheet from said wax backing, dipping said hacking into asupercooled liquid thereby causing said laminations to separate fromsaid wax due to different rates of contraction, and washing saidlaminations to remove the photosensitive emulsion therefrom.

6. A process for manufacturing small metal laminations from a sheet ofthin metal comprising cleaning a first surface of said metal, coatingsaid first surface with a photosensitive resist emulsion, placing anopaque negative having transparent lamination patterns over said coatedsurface, exposing said coated surface to light through said negative,exposing said coated surface to a developing medium which dissolves andwashes away said photosensitive resist which has not been exposed tolight thereby uncovering portions of said first surface, applying acoating of wax to a second surface of said sheet to form a relativelyrigid backing for said sheet, said wax coating having a thickness of atleast 3/32 inch, exposing said first surface to an etching medium tocompletely etch away the uncovered portions of said sheet from said waxbacking thereby leaving the laminations adhering to said backing,dipping said backing into supercooled acetone thereby causing saidlaminations to separate from said Wax, and washing said laminations toremove the photosensitive emulsion therefrom.

No references cited.

1. IN A PROCESS FOR MANUFACTURING SMALL PARTS FROM A THIN SHEET OFMETAL, THE STEPS COMPRISING COATING A SURFACE OF SAID SHEET WITH ALIGHT-SENSITIVE RESIST, EXPOSING SAID COATING SURFACE TO A LIGHT IMAGEIN THE NATURE OF A PATTERN, REMOVING THE UNEXPECTED RESIST, BACKING SAIDSHEET WITH A SUBSTANTIAL THICKNESS OF WAX, ETCHING AWAY THE METAL SHEETUNCOVERED BY THE REMOVED RESIST, AND SUPERCOOLING THE WAX BACKED PARTSTHEREBY CAUSING THE PARTS TO BE RELEASED BY THE WAX.